The effects of bovine growth hormone and thyroxine on growth rate and carcass measurements in lambs

The effects of bovine growth hormone (GH) and thyroxine (T4) on growth and carcass characteristics were assessed in Dorset ram lambs. Lambs in four groups (n = 10/group) were treated for 30 d as follows: controls, 3.33 mg (6 IU) GH/d (s.c.); 5-mg T4 implant (s.c.) on d 1 and a 10-mg T4 implant 21 d later; GH + T4. Blood samples were collected at 3-d intervals for analysis of GH, T4, triiodothyronine, somatomedin-C and testosterone concentrations. Six lambs/group were slaughtered for carcass measurements and composition. Daily GH injections increased (P less than .005) baseline plasma GH levels 10-fold, whereas plasma T4 concentrations were increased 10% (P less than .10) by the implants. Somatomedin-C increased with time in all groups, but the increments from d 0 to d 30 were higher (P less than .05) with GH treatment. Average daily gain (mean = 352 g/d), feed consumption and feed to gain ratio were not affected (P greater than .1) by GH or T4 treatment in ram lambs. Hot carcass weight and dressing percentage were increased (P less than .05) by T4. Growth hormone increased carcass protein content (P less than .005) and muscle weights while reducing carcass fat (P less than .05). Carcass composition was not altered by T4 alone, and the T4 x GH interaction was not significant; however, the combination of T4 and GH resulted in greater muscle and protein weight than did either hormone alone or no hormone administration. There were no differences in bone length or in the metacarpal growth plate width among groups. The beneficial effects of GH on carcass composition were not further enhanced by administration of thyroxine.     

Serum concentrations of thyroxine and 3,5,3'-triiodothyronine in dogs before and after administration of freshly reconstituted or previously frozen thyrotropin-releasing hormone

Concentrations of serum thyroxine (T4) and 3,5,3'-triiodothyronine (T3) were determined after the administration of freshly reconstituted thyrotropin-releasing hormone (TRH), reconstituted TRH that had been previously frozen, or thyrotropin (TSH) to 10 mature dogs (6 Greyhounds and 4 mixed-breed dogs). Thyrotropin-releasing hormone (0.1 mg/kg) or TSH (5 U/dog) was administered IV; venous blood samples were collected before and 6 hours after administration of TRH or TSH. Concentrations of the T4 and T3 were similar (P greater than 0.05) in serum after administration of freshly reconstituted or previously frozen TRH, indicating that TRH can be frozen at -20 C for at least 1 week without a loss in potency. Concentrations of T4, but not T3, were higher after the administration of TSH than they were after the administration of TRH (P less than 0.01). Concentrations of T4 increased at least 3-fold in all 10 dogs given TSH, whereas a 3-fold increase occurred in 7 of 10 dogs given freshly reconstituted or previously frozen TRH. Concentrations of T4 did not double in 1 dog given freshly reconstituted TRH and in 1 dog given previously frozen TRH. Concentrations of T3 doubled in 5 of 10, 2 of 10, and 5 of 10 dogs given TSH, freshly reconstituted TRH, or previously frozen TRH, respectively. Results suggested that concentrations of serum T4 are higher 6 hours after the administration of TSH than after administration of TRH, using dosage regimens of 5 U of TSH/dog or 0.1 mg of TRH/kg.(ABSTRACT TRUNCATED AT 250 WORDS)     

Growth and carcass characteristics and serum growth hormone, prolactin and insulin profiles in Debouillet lambs treated with ovine growth hormone and(or) zeranol

Sixteen Debouillet wether lambs (approximately 3 mo old) were placed indoors in 1.5- x 3-m pens (14 h light:10 h dark) 28 d after weaning. Lambs received no implant or a 12-mg zeranol implant on d-2 (eight lambs/group). Two days later (d 0), animals received either 0 or 2.5 mg ovine growth hormone (oGH, eight lambs/group) s.c. on alternate days for 42 d. Animals had ad libitum access to water, salt, mineral and a pelleted alfalfa diet (16% CP). After 42 d, lambs were slaughtered to evaluate carcass traits, organ weights and femur characteristics. Zeranol by oGH interactions were not detected (P greater than .20). Zeranol increased (P less than .05) BW, improved (P less than .05) feed:gain during the first 20 d and increased (P less than .10) feed intake during the last 22 d of the 42-d trial compared with controls. Carcass characteristics were not altered (P greater than .10) by 12 mg zeranol. Serum insulin and prolactin were elevated (P less than .05), but serum GH was not influenced by zeranol compared with controls. Exogenous oGH decreased feed intake (P less than .10) and improved feed:gain (P less than .05) during the initial 20 d compared with controls, but did not influence (P greater than .20) these variables during the last 22 d of the study. Carcass traits were not influenced (P greater than .10) by oGH. Exogenous ovine GH dramatically elevated (P less than .05) serum GH, but did not affect serum insulin or prolactin (P greater than .10).(ABSTRACT TRUNCATED AT 250 WORDS)     

Source and level of supplemental protein for growing lambs

Two 3 x 2 factorial growth trials and a companion metabolism trial with 13, 15, or 17% dietary CP (DM basis), with or without 3% of the DM replaced with slowly degraded menhaden fish meal, were conducted to determine if level of dietary protein influences whether slowly degraded protein improves lamb growth and protein use. The growth trials included 32 and 34 pens of two weanling lambs initially weighing 23 to 26 kg and fed for 42 d. The metabolism trial included 12 additional lambs fed in metabolism cages with a 2-wk adjustment period, a 1-wk preliminary period, and a 7-d collection period. Plasma urea N (PUN) was measured in all lambs at the conclusion of the second growth trial and at the end of the metabolism trial. There was a protein level x protein source interaction (P = 0.05) for PUN of the 12 lambs in the metabolism trial but not for the 68 lambs in the second growth trial. Replacement of part of the soybean meal protein with protein from fish meal did not affect ADG or G:F at any protein level, but it lowered (P = 0.08) PUN in the second growth trial. Plasma urea N values were higher (P = 0.002) in lambs fed diets with 15 or 17% CP; however, ADG (P = 0.037 in Exp. 1 and P = 0.055 in Exp. 2), and G:F (P = 0.094 in Exp. 1 and P = 0.003 in Exp. 2) were lower for lambs fed the diets with 13% CP. There was little difference in ADG or G:F between lambs fed the diets with 15 or 17% CP, suggesting that a CP level of 15% with supplemental protein from soybean meal would be optimal for 25- to 40-kg growing Finnsheep x Dorset lambs.     

Effect of feeding thyrotropin-releasing hormone to lactating sows

Two experiments were conducted to assess the effects of feeding thyrotropin-releasing hormone (TRH) during lactation on sows. In Exp. 1, sows were fed 0, 1, 10, 100 or 1,000 mg TRH on d 10.8 +/- .4 (mean +/- SE) after parturition. Blood samples were taken from sows every 30 min from -2 h to 8 h and at 10, 12 and 18 h from feeding. Consumption of 100 or 1,000 mg TRH increased mean serum concentrations of thyroxine (T4; P less than .001), 1,000 mg TRH increased growth hormone (GH; P less than .06) and 100 or 1,000 mg TRH increased prolactin (PRL; P less than .01), but insulin (INS; P greater than .10) was unaffected by TRH. Serum concentrations of T4 were elevated within 2 to 4 h after feeding TRH and remained elevated for 12 to 18 h. Concentrations of GH and PRL began to increase immediately after feeding 100 or 1,000 mg TRH and remained elevated for 6 and 8 h, respectively. In Exp. 2, sows were fed 0 or 200 mg TRH from d 111 of gestation to weaning at 27.1 +/- .3 d of lactation. Consumption of TRH elevated concentrations of T4 at all stages of lactation and increased respiration rate on d 10 and d 20, heart rate on d 20, and milk production on d 20 of lactation. Consumption of TRH did not influence number of pigs born, number born alive, survival rate during lactation, sow body weight, heartgirth, backfat depth, feed disappearance, or milk production on d 10 of lactation. Piglets nursing sows fed TRH were similar in weight to piglets nursing sows not fed TRH on d 0 and 5 of lactation, but they were heavier on d 10 (P less than .07), 15 (P less than .001), 20 (P less than .001) and 27 (P less than .0001). Sows fed TRH took longer (P less than .001) to return to estrus after weaning than control sows. Results indicated that feeding TRH elevated T4, GH and PRL and that feeding TRH for the duration of lactation increased milk production on d 20 of lactation and increased weaning weights, but it delayed estrus after weaning.     

Serum concentrations of thyroxine, 3,5,3'-triiodothyronine, thyrotropin, and prolactin in dogs before and after thyrotropin-releasing hormone administration

Serum concentrations of thyrotropin (TSH), prolactin, thyroxine, and 3,5,3'-triiodothyronine in 15 euthyroid dogs and 5 thyroidectomized and propylthiouracil-treated dogs after thyrotropin-releasing hormone (TRH) administration were measured. Although thyroidectomized and propylthiouracil-treated dogs had higher (P less than 0.01) base-line concentrations of TSH in serum than did euthyroid dogs, concentrations of TSH after TRH administration varied at 7.5, 15, and 30 minutes with 14 of 45 samples obtained from healthy dogs having lower TSH concentrations than before TRH challenge. Similarly, concentrations of 3,5,3'-triiodothyronine in the serum of euthyroid dogs 4 hours after TRH administration were similar (P less than 0.05) to concentrations before TRH challenge. Although the mean concentration of thyroxine in serum was elevated (P less than 0.05) 4 hours after administration of TRH to euthyroid animals, as compared with base-line levels, the individual response was variable with concentrations not changing or decreasing in 4 dogs. Therefore, the TRH challenge test as performed in the current investigation was of limited value in evaluating canine pituitary gland function. Although mean concentrations of TSH in serum were higher (P less than 0.05) in euthyroid dogs after TRH administration, the response was too variable among individual animals for accurate evaluation of pituitary gland function. Concentrations of prolactin in the sera of dogs after TRH administration, confirmed previous reports that exogenously administered TRH results in prolactin release from the canine pituitary and indicated that the TRH used was biologically potent.     

Growth performance and carcass composition of lambs infused for 28 days with a growth hormone-releasing factor analogue.

A human growth hormone-releasing factor analogue, [DesNH2Tyr1,D-Ala2,Ala15]hGRF(1-29)NH2 (GRF-A), was infused s.c. into lambs for 28 d to determine its effects on growth performance and carcass composition. Twenty crossbred wethers weighing 47.0 +/- .5 kg were implanted with 7-d osmotic minipumps at weekly intervals. Minipumps contained either vehicle (dimethyl sulfoxide:H2O, 1:1) or GRF-A, released at a rate of 208 pmol (or .7 micrograms).h-1.kg-1. During the infusion period, plasma GH levels were increased (P less than .01) in GRF-A-treated wethers compared with control wethers (15.0 vs 9.3 ng/ml) and were higher on days that closely followed minipump implantation. Plasma IGF-I and hepatic IGF-I RNA concentrations were similar in lambs of both groups. Analogue treatment improved feed conversion (4.9 vs 5.8 kg dry matter/kg gain, P less than .05), increased average daily gain (.35 vs .30 kg, P = .05) and had no effect on feed intake, wool growth and body, carcass, selected organ and pituitary weights. Carcasses from GRF-A-infused lambs had less adjusted fat depth, a lower percentage of fat and a higher percentage of protein (P less than .05) than carcasses from control lambs. Magnitude of most effects of GRF-A on carcass measurements were correlated with the mean GH level that a lamb had during the infusion period. In conclusion, s.c. infusion of GRF-A improved feed utilization and altered carcass composition of feeder lambs in a relatively short period of time (28 d).     

Effect of prenatal trenbolone acetate treatment on lamb performance and carcass characteristics

Forty-three pregnant Dorset and Dorset crossbred ewes were assigned randomly to a control group or implanted with either 300 mg trenbolone acetate (Low TBA) or 1,200 mg trenbolone acetate (High TBA) between d 40 and 60 of gestation. Adjusted weaning weights for ewe lambs were 23.3% less (P less than .10) with vs without TBA treatments. Postweaning ADG of ewe lambs was lower (P less than .05) but ADG of ram lambs was greater (P less than .05) for high TBA vs low TBA. Ewe lambs receiving high TBA had 19% less (P less than .05) gain per unit of feed than those receiving low TBA. Days on test for ewe lambs was greater (P less than .05) due to TBA treatment and for high TBA vs low TBA. Days on test for ram lambs was decreased (P less than .05) due to high TBA compared to low TBA. Subcutaneous fat over the ribeye and lower rib were greater (P less than .05) for high-TBA ewe lambs vs low-TBA ewe lambs. Percentage kidney and pelvic fat of ewe lambs was lower (P less than .05) due to TBA treatments. Ribeye area per unit of carcass weight was lower (P less than .05) in high-TBA ewe lambs vs low-TBA ewe lambs. Yield grade of ewe lambs was lower (P less than .05) for low TBA vs high TBA. Prenatal trenbolone acetate treatment of ewe lambs did not improve their subsequent postnatal growth performance and carcass traits. In addition, TBA implantation of the pregnant ewe produced dystocia and less milk production, as evidenced by the need for more lambs to be grafted.     

Effects of plane of nutrition, growth hormone and unsaturated fat on growth hormone, insulin and prolactin receptors in prepubertal lambs

The influence of plane of nutrition, growth hormone (GH) treatment and dietary polyunsaturated fat on serum concentrations of GH and insulin (INS) and binding capacities of GH, INS and prolactin (PRL) in liver, mammary parenchyma and adipose tissue was assessed in prepubertal ewe lambs. Ten lambs were assigned to each of four treatment groups. Treatments included: (A) lambs with ad libitum access to a high-energy ration; (G) lambs fed as group A and treated with bovine GH (.08 mg/kg/d); (R) lambs with feed intake restricted to limit ADG to about 120 g; and (S) lambs with ad libitum access to a ration including formaldehyde-protected sunflower seed. Diets, all approximately isonitrogenous and isocaloric, were fed from about 7 to 22 wk of age. Weekly blood samples were collected during wk 6 to 14 of the trial. Averaged across sampling dates, mean serum concentrations of GH were elevated in G lambs (P less than .05) and INS concentrations differed in the order G greater than A greater than R = S (P less than .05). Crude membranes for binding assays were prepared from liver, mammary parenchyma and adipose tissue. Mean concentrations of GH receptors in liver and PRL receptors in mammary parenchyma were elevated in group S lambs (P less than .01). Dietary polyunsaturated fat increased the number of GH receptors in liver and PRL receptors in mammary parenchyma. Increased availability of receptors may mediate the stimulation of mammary growth observed in lambs fed polyunsaturated fat.     

Dietary fatty acids modulate hormone repsonses in lactating cows: Mechanistic role for 5′-deiodinase activity in tissue

Supplemental dietary fat provides excess fatty acids (FA), which can alter circulating concentrations of several hormones. To test the effects of fatty acid isomer type and possible sites of regulation, we abomasally infused fat mixtures high in cis-C_18:1 FA (iTRS) or no infusion (NI) and performed intravenous arginine (ARG) and intramuscular thyrotropin-releasing hormone (TRH) challenges. The experimental design was a replicated 3 × 3 Latin square. Challenges were conducted on Days 10 (ARG) and 12 (TRH) after initiation of fat infusion on each of three 4-wk experimental periods. Plasma concentrations of IGF-I were lower (P < 0.01) when cows received iCIS or iTRS compared with NI. Plasma insulin concentrations increased with ARG but responses were not affected by FA. Plasma growth hormone (GH) was unchanged after ARG. Peak plasma GH and thyroid-stimulating hormone (TSH) responses to TRH were blunted (P < 0.05 and P < 0.1, respectively), whereas thyroxine (T₄) and triiodothyronine (T3) responses were augmented post-TRH (P < 0.01) when cows received either FA isomer. Prolactin responses to TRH were not different between infusion treatments, although basal plasma concentrations before TRH were higher in cows infused with iTRS (P < 0.05). To focus on fat regulation of the thyroid axis, we tested directly in vitro the ability of fatty acids dissolved with sodium taurocholate to affect Type-I 5'-deiodinase (5'D) activity in bovine liver homogenates. Homogenate 5'D was not affected by C_2:0---C10:0 fatty acids, but decreased linearly (P < 0.01) with increasing concentrations of C_12:0---C_16:0 and C_18:1 isomers. CisC_18:1 decreased 5′D more than the trans-isomer (P < 0.01), the difference was only apparent at concentrations greater than 0.25 mM. The data suggest that various aspects of pituitary hormone regulation are differentially affected by FA composition. Fatty acid infusion may accentuate end organ responses in the thyroid axis and decrease IGF-I in the somatotropic axis. The data also suggest that FA isomer may alter patterns of extrathyroidal generation of thyroid hormones via direct influences on 5′D.     

Effects of long-term administration of pituitary-derived bovine growth hormone and estradiol on growth in steers

Sixty-three Friesian steers (9 mo old, 257 kg; n = 15 or 16/treatment) were employed in a 2 x 2 factorial to test bovine growth hormone (bGH) and estradiol (Compudose implant). Steers received daily subcutaneous injections of vehicle or bGH (40 micrograms/kg body weight) for 22 wk. Steers were slaughtered 8 wk after the end of bGH treatment (wk 30). Steers had ad libitum access to silage plus a fixed amount (4 to 5.5 kg/d) of concentrate. Average daily gain (ADG) and feed conversion efficiency (FCE) improved (P less than .05) in response both to bGH and to estradiol during wk 0 to 22. Although bGH did not affect ADG or FCE during wk 23 to 30, estradiol improved (P less than .05) them; bGH and estradiol appeared additive (nonsignificant interactions) during wk 0 to 22. At slaughter, estradiol increased (P less than .05) carcass weight and carcass and leg length while decreasing (P less than .05) conformation score and percentage of kidney, knob and channel fat (KHP); bGH decreased (P less than .05) KHP. Although both bGH and estradiol increased (P less than .01) plasma GH, their effects were not additive. Both bGH and estradiol increased (P less than .01) plasma somatomedin-C and decreased (P less than .01) plasma urea nitrogen concentrations; effects were additive. Estradiol, but not bGH, increased (P less than .05) plasma glucose, whereas neither bGH nor estradiol altered plasma creatinine and nonesterified fatty acids. In summary, both bGH and estradiol improved growth and FCE, and their effects appeared to be additive. It is likely that some of their effects were mediated by somatomedin-C.     

Thyroid function in the cat: assessment by the TRH response test and the thyrotrophin stimulation test

Changes in total thyroxine (T4), free T4 and total tri-iodothyronine (T3) were measured in 13 cats after the intravenous injection of varying doses of thyrotrophin stimulating hormone (TSH) (0–5 U/cat n = 6; 1 U/cat n = 8; 1 U/kg bodyweight, n = 7) or thyrotrophin releasing hormone (TRH) (100 ug/cat, n = 10). All three doses of TSH resulted in a significant (P < 0–05) rise in T4, free T4 and T3 levels, with the mean peak in hormone concentrations occurring six to eight hours after injection. The three doses of TSH all appeared to produce maximal stimulation of thyroid hormone secretion. The mean percentage increase in hormone concentrations at seven hours following the three doses of TSH ranged from 167 to 198 per cent for T4, 240 to 365 per cent for free T4, and 73 to 116 per cent for T3. Following administration of TRH there was also a significant (P < 0–05) rise in T4, and free T4. The mean peak in T4 and free T4 levels occurred at four hours, and mean increases in hormone levels at this time were 92 per cent for T4, and 198 per cent for free T4. The administration of TRH produced little change in T3 levels. TSH administration resulted in a significantly higher (P < 0–05) percentage peak increase in T4, free T4 and T3 levels at all three dosages than did TRH.     

Effects of oral chlortetracycline and dietary protein level on plasma concentrations of growth hormone and thyroid hormones in beef steers before and after challenge with a combination of thyrotropin-releasing hormone and growth hormone-releasing hormone.

The objective of this study was to determine the effect of a subtherapeutic level of chlortetracycline (CTC) fed to growing beef steers under conditions of limited and adequate dietary protein on plasma concentrations of GH, thyroid-stimulating hormone (TSH), and thyroid hormones before and after an injection of thyrotropin-releasing hormone (TRH) + GHRH. Young beef steers (n = 32; average BW = 285 kg) were assigned to a 2x2 factorial arrangement of treatments of either a 10 or 13% crude protein diet (70% concentrate, 15% wheat straw, and 15% cottonseed hulls) and either a corn meal carrier or carrier + 350 mg of CTC daily top dressed on the diet. Steers were fed ad libitum amounts of diet for 56 d, and a jugular catheter was then placed in each steer in four groups (two steers from each treatment combination per group) during four consecutive days (one group per day). Each steer was injected via the jugular catheter with 1.0 microg/kg BW TRH + .1 microg/kg BW GHRH in 10 mL of saline at 0800. Blood samples were collected at -30, -15, 0, 5, 10, 15, 20, 30, 45, 60, 120, 240, and 360 min after releasing hormone injection. Plasma samples were analyzed for GH, TSH, thyroxine (T4), and triiodothyronine (T3). After 84 d on trial, the steers were slaughtered and the pituitary and samples of liver were collected and analyzed for 5'-deiodinase activity. Feeding CTC attenuated the GH response to releasing hormone challenge by 26% for both area under the response curve (P<.03) and peak response (P<.10). Likewise, CTC attenuated the TSH response to releasing hormone challenge for area under the response curve by 16% (P<.10) and peak response by 33% (P<.02), and attenuated the T4 response for area under the curve by 12% (P<.08) and peak response by 14% (P<.04). Type II deiodinase activity in the pituitary was 36% less (P<.02) in CTC-fed steers than in steers not fed CTC. The results of this study are interpreted to suggest that feeding subtherapeutic levels of CTC to young growing beef cattle attenuates the release of GH and TSH in response to pituitary releasing hormones, suggesting a mechanism by which CTC may influence tissue deposition in cattle.     

Equine thyroid function tests: a preliminary investigation.

A similar and significant (P less than 0.001) increase in plasma thyroxine (T4) concentration was seen in seven clinically normal thoroughbred horses 2 h after the intravenous administration of either 2.5 iu or 5 iu of thyroid stimulating hormone (TSH) with a peak response around 4 h after administration. The intravenous administration of 0.2, 0.5 or 1 mg thyrotrophin releasing hormone (TRH) resulted in a significant (P less than 0.01) increase in T4 concentration in three groups of animals; six thoroughbreds in full work, five thoroughbreds at rest and four ponies at rest. The peak response was recorded at 3 or 4 h after administration. A significant difference between the groups in the degree of response to TRH was only found between the thoroughbreds in work and those at rest with 1 mg TRH (P less than 0.05). When two additional ponies were investigated in a similar way, a reduced response to TRH was observed: a pregnant mare had a similar response to 5 iu TSH as the thoroughbreds; the other pony also showed a lowered response to TSH. In a group of 2- or 3-year-old thoroughbreds in training no difference in the T4 response 4 h after intravenous administration of 0.5 mg TRH could be determined, according to the month, age, sex or work intensity. Although resting T4 concentrations did not differ significantly between animals believed to be suffering from the equine rhabdomyolysis syndrome (ERS) and those suffering from a variety of other conditions, some ERS sufferers may have a lowered response to TRH.     

Temporal patterns of growth hormone, prolactin and thyrotropin secretion in Targhee rams selected for rate and efficiency of gain

Thirteen Targhee rams selected for rate and efficiency of gain for 4 yr (1.5 generations) were compared with 10 rams from a Targhee line with no selection for over 20 yr to determine if selection for these traits would be associated with changes in the secretion of growth hormone (GH), thyrotropin (TSH) and(or) prolactin (PRL). Selected rams exhibited greater birth weight, average daily gain (ADG) and feed consumed/day during a 6-wk individual feeding regimen, and exhibited greater overall ADG during a 16-wk feeding trial as compared with the unselected rams. Temporal blood plasma samples were collected at 15-min intervals for 8 h from each of the 23 rams for hormone analysis. Selected rams exhibited greater overall mean GH (6.1 +/- .4 vs 4.6 +/- .5 ng/ml), overall mean TSH (8.6 +/- 1.2 vs 6.2 +/- .7 ng/ml) and baseline mean TSH (8.0 +/- 1.1 vs 5.6 +/- .5 ng/ml) than the unselected rams. Although the adjusted GH spike amplitude value was higher in the selected line (12.1 +/- 3.0 vs 7.4 +/- .8 ng/ml), this difference was not significant. No differences were observed with any of the variables of PRL secretion. In addition, there were no significant correlations between any of the hormone variables and any of the feed or gain data. These data support the hypothesis that Targhee rams selected for rate and efficiency of gain exhibit higher plasma levels of GH and TSH than unselected rams of the same breed.     

Effect of whole-crop pea (Pisum sativum L.) silages differing in condensed tannin content as a substitute for grass silage and soybean meal on the performance, metabolism, and carcass characteristics of lambs

Two experiments were conducted to investigate the effect of inclusion of whole-crop pea (WCP) silages, differing in condensed tannin content, as a substitute for grass silage (GS) and soybean meal on lamb metabolism, performance, plasma metabolites, digestibility, and carcass characteristics. In both experiments lambs were offered either solely GS or a 50:50 mix on a DM basis of GS with either low-tannin (LTPS) or high-tannin (HTPS) pea silage ad libitum. Each forage mix was fed with either 400 g/d of low-protein (LP) concentrate or 400 g/d of LP with an additional 200 g/d of pelletized soybean meal (HP), resulting in 6 dietary treatments. Experiment 1 examined the effects of the diets on metabolism, digestibility, and N balance using 6 lambs in 4 periods of 21 d in an incomplete crossover design. Experiment 2 used 48 lambs and examined the effects of the diets on ADG, plasma metabolites, and carcass characteristics over 56 d. Both experiments were analyzed using a 3 × 2 factorial arrangement of treatments. In Exp. 1, lambs offered the LTPS diets had a greater (P < 0.05) digestibility of DM and OM than those offered the GS diets. Lambs offered the WCP silages had an increased (P < 0.05) N intake, N output, and digestibility of GE compared with those offered GS. Mean N digestibility was greatest (P < 0.05) in lambs offered LTPS. Lambs offered HP diets had increased (P < 0.001) digestibility of DM, OM, GE and N, and N- intake, output, retention, and digestibility compared with those offered the LP diets. In Exp. 2, there was no effect (P > 0.05) of forage type on intake, slaughter BW, or feed conversion efficiency (FCE). However, lambs offered the LTPS had a greater (P < 0.05) ADG than those offered the GS diets. Feeding diets containing HP increased (P < 0.001) total DMI, slaughter BW, ADG, and FCE. Lambs offered the WCP had a greater (P < 0.05) plasma β-hydroxybutyrate and urea concentration compared with those offered the GS diets. Feeding lambs HP diets increased (P < 0.05) plasma urea and total protein. Forage mix had no effect (P > 0.05) on carcass composition except for fat depth, which was greater (P < 0.05) in lambs offered WCP silage. Diets containing the HP increased (P < 0.05) carcass weight, hind leg circumference, chop dimensions, and kidney weight. It was concluded that lambs offered LTPS performed better than those offered GS and that LTPS has a concentrate sparing effect. Additionally, the increased tannin concentration in HTPS did not increase performance over lambs offered either GS or LTPS.     

Effects of bovine somatotropin and thyroid hormone status on hormone levels, body weight gain, and mohair fiber growth of Angora goats.

Forty-eight Angora goats (24 wethers and 24 doelings; 5 mo old; 16 +/- 0.5 kg initial BW) were used in an experiment with a 2 x 3 factorial treatment arrangement (n = 8) to evaluate effects of recombinant bovine somatotropin (bST) administration and thyroid hormone status (euthyroid, hypothyroid, and hyperthyroid) on hormone levels, ADG, and mohair fiber growth. The bST was a slow-release zinc-based suspension, with sustained delivery (100 microg/[kg BW x d]) over a 14-d period. Hyperthyroidism was maintained by daily treatment with thyroxine (T4; 150 microg/[kg BW x d]), and hypothyroidism was achieved by feeding 6 mg/(kg BW x d) of propylthiouracil. The experiment was conducted in July to September and consisted of a 2-wk pretreatment period and 8 wk of bST treatment. Goats were given ad libitum access to a diet with 15% CP and 2.54 Mcal/ kg ME (DM basis). Concentrations of T4 and T3 were greatest (P < 0.01) among treatments for hyperthyroid-bST and hyperthyroid-control (T4: 38.6 and 38.0 microg/dL; T3: 406 and 385 ng/dL, respectively); similar among euthyroid-control, euthyroid-bST, and hypothyroid-bST (T4: 11.1, 11.5, and 9.8 microg/dL, respectively; T3: 232, 252, and 226 ng/dL, respectively); and lowest (P < 0.01) for hypothyroid-control (T4: 5.1 microg/dL; T3: 144 ng/dL). Plasma concentration of insulin-like growth factor-I was greatest (P < 0.01) for euthyroid-bST (596 ng/mL) and hypothyroid-bST (618 ng/mL); however, concentration for hyperthyroid-bST was similar to those for euthyroid-control, hypothyroid-control, and hyperthyroid-control (188, 178, 187, and 191 ng/mL, respectively). Dry matter intake was greatest (P < 0.05) for euthyroid-bST (794 g/d), similar among hypothyroid treatments (693 and 703 g/d for control and bST, respectively) and euthyroid-control (681 g/d), and lowest for hyperthyroid groups (554 and 518 g/d for control and bST, respectively); ADG for hyperthyroid goats (11 g/d) was lower than with hypothyroidism and euthyroidism (72 and 73 g/d, respectively); and mohair fiber growth was greater (P < 0.01) for hyperthyroidism (0.133 g/[100 cm2 x d]) than for hypothyroid and euthyroid goats (0.102 and 0.104 g/[100 cm2 x d], respectively). Hyperthyroidism also increased mohair length growth rate by 15% and decreased fiber diameter by 7.8% (P < 0.01). These results demonstrate interactions between growth hormone administration and thyroid hormone status, although these influences had limited effects on ADG and mohair fiber growth.     

Fattening ability and carcass value of Dhamari and Tehami ram lambs,F1 crossbreds of Dhamari × Tehami in Yemen

A fattening experiment was carried out to analyze and evaluate the effect of ram lamb genotype on the growth, feed conversion (FC), and carcass value of Dhamari ram lambs, F1 crossbreds of Dhamari?×?Tehami (F₁ DhT), and Tehami ram lambs. Genotype of the ram lambs including the experiment (n?=?30) had high significant effect on total weight gain (TWG), average daily gain (ADG), and FC (P?P?P?P?P?P?P?1 DhT was better than Tehami ram lambs in ADG, TWG, and FC. Additionally, the results show that the feed conversion was in F₁ DhT crossbreds ram lambs better than pure Dhamari and Tehami ram lambs, mainly in the carcass indicators.     

Effect of immunization against somatostatin in the pregnant ewe on growth and endocrine status of the neonatal lamb

Absorption of somatostatin (SRIF) specific antibodies from colostrum of ewes actively immunized against SRIF may improve growth rate of the neonatal lamb by neutralizing the inhibitory effects of SRIF on pituitary and thyroid function. Growth and endocrine parameters in the offspring of SRIF immunized (SI) and control (C) crossbred ewes were examined. Lamb weight was recorded at birth and twice each week to 24 days of age. Blood samples were collected prior to first suckle and twice each week. At 21 to 24 days of age, in separate experiments, lambs were infused with glucose (0.29 g/kg), arginine (0.25 g/kg) or thyrotropin-releasing hormone (TRH; 0.33 microgram/kg). A strong correlation (R = 0.88; P less than .01) was observed between anti-SRIF titre in the ewe at parturition and in the lamb at 3 days of age. No effect on lamb birth weight (SI 4.28 +/- 0.27 kg; C 4.35 +/- 0.23 kg) was observed. At 24 days of age cumulative gain in SI lambs (5.4 +/- 0.32 kg) was greater (P less than .05) than in C lambs (4.5 +/- 0.32 kg). The growth hormone secretory responses to glucose or arginine were not affected by treatment. Plasma IGF-I, plasma thyroxine (T4) and the plasma thyrotropin and T4 responses to TRH were not different between treatments. Plasma triiodothyronine (T3) was higher (P less than .05) in SI (2.46 +/- .10 ng/ml) than in C (2.01 +/- .05 ng/ml) lambs, however, the plasma T3 response to TRH was lower in SI lambs. Plasma glucose (mg/dl) was higher (P less than .05) in SI (118.4 +/- 1.7) than in C (106.0 +/- 4.0) lambs. Plasma insulin was not affected by treatment. Increased plasma T3 and glucose concentrations during SRIF immunoneutralization in the neonate lamb may be important factors contributing to the growth response observed.     

Skeletal muscle protein synthesis and growth hormone secretion in young lambs treated with clenbuterol

To determine effects of clenbuterol (CB) on muscle protein turnover and growth hormone (GH) secretion, 16 crossbred wether lambs (14.4 kg) were randomized into two groups designated to receive daily oral boluses of gelatin capsules containing corn starch with either 0 (control, CTL) or 1.87 mg/kg body weight CB for either 14 (n = 8) or 28 d (n = 8). This calculates to be approximately 40 mg CB/kg diet. Lambs had ad libitum access to a 16% crude protein corn-soy diet and feed consumption (FC) was measured. After 14 and 28 d, lambs were slaughtered and semitendinosus (ST), longissimus (LD) and brachialis (BR) muscles were exercised, weighed and analyzed for protein (TP) content. For 6 h prior to slaughter of 28-d lambs, 2.5 microCi L-[U-14C]tyrosine/kg was infused intravenously, blood was sampled and plasma was analyzed for specific radioactivity of tyrosine. Plasma GH concentrations were assessed by radioimmunoassay. No differences due to treatment were found in FC, rate of gain or GH concentrations. Semitendinosus and BR weights of control lambs at 14 d did not differ between treatments. At 28 d, ST and BR weights of control lambs (58.8 and 18.5 g, respectively) were less (P less than .10) than those of lambs treated with CB (74.3 and 23.1 g, respectively). The TP per ST and BR at 28 d for control lambs was 71.5 and 85.1% (P less than .10) that of muscles of lambs treated with CB. Fractional protein synthesis rates (FSR) of the BR (9.4 vs 6.1%/d) and total protein synthesized in ST muscle per day (1.4 vs .8 g) were elevated (P less than .10) in lambs treated with CB compared to controls. These data suggest that the increased fractional accretion rate observed in lambs treated with CB for 28 d was caused by increased FSR.